Bugfixes:
- Align Python floats with xsd:decimal rather than xsd:double, finally, because decimal accepts int too
- Fix Class.instances() so as it returns instances of subclasses (as indicated in the doc)
- Fix direct assignation to Ontology.imported_ontologies
- Fix a bug in reasoning, when adding deduced facts between one loaded and one non-loaded entity
- Fix search(prop = "value") when value is a string and the ontology uses localized string